The background of this invention delves into the arena of valves used to control the flow of fluids, especially water. Water being a unique fluid due to it's noncompressability and it's ability to be present in 2 forms at room temperature (liquid and vapor). Emphasis has been placed on using valves in piping structures as a means for isolating or shutting off flow to particular areas. Heating and cooling within climate zones have been controlled by starting and stopping fluid control into piping structures, with the associated pumps often cycling with the valves. With the costs of energy rising, current emphasis is on using valves to act as precision temperature controllers, regulating the flow of chilled or heated water into and out of piping structures, reducing the load on the pumps and heating and cooling units thereby decreasing energy demands, while maintaining properly controlled climate zones. Therefore, the type of valve necessary for this application needs to possess unique characteristics.
There are basically two types of valves used in the application of water handling; those using a vertical displacement of the sealing mechanism and those using a horizontal or rotational displacement of the sealing mechanism.
Vertically displaced valve include globe and gate valves, where the sealing member either plunges into a slot or where a plug is compressed onto a seat. Both devices have similar operating characteristics and also have similar problems. The sliding stem of the valve moves vertical through sealing o-rings and packing glands. The sliding stem movement tends to drag along creating leaks thereby shortening the life of the sealing system. In order to prevent this leakage, more sealing and packing glands are used overly constraining the stem movement effecting the controllability of the valve. Due to friction damage, these o-rings and packing glands require frequent maintenance and replacements. O-rings are best used for rotational sealing application and are often used as wipers to prevent contamination, but often roll up and cease when subjected to vertical motion, especially when subjected to a large pressure difference between the sealing surfaces of the O-Ring. High pressure is also to the cause of valve stem blowout, as there is little to protect the valve stem from acting in the normal vertical manner, only escaping the parameters of the valve stem run. As there are many turns necessary to move the valve between it's open and closed positions, more control can be exhibited, but these many turns also lead to hysteresis and deadband as there is a range through which an input signal can be varied, upon reversal of direction, without initiating an observable change in the output signal. This sensitivity or mean static gain is compounded by hysteresis of the valve causing inaccuracy of the control of the valve, especially in the presence of high pressure which causes the sealing member to be more difficult to position. At higher pressures striction can also occur. Striction is a combination of stick and friction, where a force large enough to overcome the striction of the valve at high pressure is too great to create a small amount of change. Striction along with the hystersis can cause a controller to cycle many times trying to achieve the proper setting. Vertically displaced valves are also difficult to control in multiple port configurations. It is almost impossible for both plugs to seat simultaneously or open to exactly the same location with one controller for 2 or more ports. Studies have shown that there can be up to a 20% overflow at 60-70% of opening between the ports, causing increased energy costs for pumping.
One of the most damaging forces that can destroy valves and the downstream piping associated with the piping system is cavitation. Cavitation is the noisy formation and subsequent collapse of water vapor formed when the pressure of a liquid drops below its vapor pressure at the vena contracta and then recovers to a pressure level above it's vapor pressure downstream of the valve. The vena contracta is the constriction part of the valve when the valve is throttled at the lower ranges of openness. The fluid on the open side of the valve attempts to “jet” past the opening of the valve in a minimal degree of openness. This is especially prevalent in vertically displaced valves as there is a longer amount of time needed to open the valve including a longer time period where cavitation can take place. This cavitation in high pressure systems can destroy the sealing member of the valve and also causes high pressure jets of fluid to directly impinge on downstream valves and piping system.
Horizontally displaced or plug valves are possibly the oldest type of valve is use today, dating back to the ancient ruins of the early Roman water systems. The plug valve has a rotating plug, through which a passsageway is defined allowing fluids to flow when the passageway is unobstructed by the walls defining the valve seat. The two main designs in use today in the high pressure applications are segmented eccentric and through hole plug valves. Segmented refers to the fact that a segment or section of the plug is removed characterizing the flow. Eccentric refers to the fact that the axis of rotation is not along the axis of the flow of the fluid, causing a leverage force upon the closing of the valve along with allowing the segment to swing clear of the walls of the valve during opening and closing reducing friction, minimalizing wear. Unfortunately, due to it's eccentric characteristic, the presence of high pressure increases the amount of force needed to open the valve, and due to it's segmented design, a high degree of caviation is present when the valve is throttled close to the closed position. This jet of fluid can actually be more harmful than with vertically displaced valves as the shape of the segment can form a lethal jet of high pressure water past the valve without any obstacles in the valve itself. The pressure difference between the high and low side of the valve in this throttled position may also suck the plug into the seat. The high pressure can also cause the segmented portion to pop out of the seat, causing a jump in the flow. Eccentric plugs are not suitable for multiple outlet port configurations as the eccentric positioning for one opening will not be suitable for other openings at the same time, making complete shutoff impossible to obtain.
The other plug valve is a through hole or ball valve. The installed flow characteristics of a normal ball valve exhibits a non-linear equal percentage relationship of how the flow in the system changes relative to changes in the valve opening. Ball valves are generally referred to as quarter turn valves as they only require one quarter of a turn to facilitate a fully open state to a fully closed state. Typical ball valves act as quick opening valves where 15% of opening of the valve can equal roughly 50% of the flow. This large amount of fluid passing through such as small opening causes jetting of the fluid and higher heat transfer through the coil, resulting in higher energy consumption. Caviation, that results due to the jetting also has a higher potential to damage than would be found in globe or gate valves. It is very difficult to control below 30% of opening as the amount of fluid flow is not directly relational to the percentage of the opening of the valve. Normal ball valves optimally work between 30 to 70% of the opening percentage and exhibit sluggish behavior beyond 70% opening. Some manufactures have designed inserts for the throughhole portion of the plug, such as Series CPT Characterized Seat Control Valves manufactured by Worcester Controls. Unfortunately, high pressures will cause these inserts to break or blow out under the pressures as their construction is less sturdy under the pressure than the surrounding plug material.
High pressures also cause high degrees of torque to open the valve. This is due to the fact that the plug or ball floats in the valve body as it is only suspended by an upper stem. In high pressures, the ball is forced upon the o-rings that prevent leakage of the valve. These high thrust loads on the o-rings cause o-ring wear due to the friction of the ball against the o-ring during the turning of the ball under pressure. This friction can also lead to deadband, as the amount of force necessary to start the movement of the ball can not be stopped fast enough for minor changes in flow. Some manufactures have created sealing systems where o-ring are pre-loaded in tension against the ball though a series of metal springs, so that the o-rings will always be in contact with the ball as disclosed in U.S. Pat. No. 4,292,989 issued to Cazzaniga et al on Oct. 6, 1981 and in U.S. Pat. Nos. 5,624,101, 5,542,645 and 5,494,256 issued to Benson.
Another problem with the current prior art of quick opening valves is the effects on the efficiencies of the coils or piping systems that the valves are intended to regulate. One application of the valve is to control the amount of fluid flowing into coils of heating and cooling systems. Current state of the art valve cause inefficient heat transfers by causing a large percentage of heat transfer or flow with only a minimal opening of the valve. This lack of fine control at the lower percentage of valve opening requires the continual cycling of heating and cooling systems, further exacerbating the wear and destruction of the sealing components of the valve.
In low flow, high pressure situations, the difference in pressures between the high side and the low side of the ball can create a venturi effect on the low side of the ball, sucking these extended o-rings out of position. Some manufactures have designed a trunnion apparatus to support the ball from the upper and lower extremes. This trunnion design increases the number of o-rings as the stems are incorporated into the actual ball and the entire unit moves. Repeated actuations of the valve will cause o-ring and packing gland wear as with the vertically displaced valves leading to leakage and maintenance issues. This creates problems as the entire ball and stems must be removed as one to replace the o-rings on the stems thereby causing re-assembly issues with the presence of the o-rings that surround the actual ball itself. The cost of casting and machining of these stem and valve apparatuses is very high and tolerances are very small.
As described, there are problems with the current state of the industry involving precision control of valves. Leakage through worn or displaced o-rings causes false reading in the control systems causing energy to be wasted in powering the pumps and in the actual piping system as well. These false reading cause fluxations in temperature causing discomfort to the users, along with the environmental concerns of corrosive or toxic fluids escaping through failing o-rings and valves. To combat leakage, more o-rings and packing glands are required which increases friction or striction. This friction requires more torque from the actuators and more power consumption, or operators are forced into larger more expensive actuators for the valves. Friction also causes more problems when combined with the naturally occurring deadband and hysteresis in valves. Poor flow characteristics causes erosion of the valve members through the effects of caviation, inaccurate control variables and non-linear equal percentage flow relationships. Compatability of low flow abilities of various valves prevent proper balancing and utilization of the piping system, that the valves were originally designed to control.
It would be advantageous to have a valve that would be able to withstand higher pressures while maintaining a low amount of torque required for it's operation, along with the inherent ability to operate at lower flow rates without the damaging effects of caviation and erosion. It would be advantageous to have this valve be maintainable without large scale disassembly, whilst the sealing member is restrained from movement. It would be advantageous to have a investment casted trunnionated spherically shaped plug valve with separable stems in a modular design decreasing assembly and manufacturing time, as a hollow ball can be subjected to minimal machining and preparation reducing fatigue and induced stresses on the actual ball. It would be advantageous to have integral with the plug equally shaped parabolic openings symmetrical about the directrix of the parabola, said openings being diametrically opposed juxtapositioned along the other side of the plug, whereby the smaller orifice or vertex of one opening is opposite the larger or apex orifice of the other opening. It would be advantageous to have a third such opening or more along the surface of the ball, to facilitate a greater number of ports for the valve. It would also be advantageous to have floating sealing members that are restricted in their movement, restrained into a specific space that will be not be effected by the presence of a high differential pressures on either side of the plug. It would be advantageous to have this trunnionated plug which is integrally enhanced with parabolically shaped flow paths, which is sealed with restrained floating o-rings to be placed within a valve housing where low amount of torque is required to precisely control temperature through the control of flow of fluids throughout piping systems.
It is an object of this invention to create a plug valve that is trunnionated with separable stem components.
It is an object of this invention to provide a plug valve with stems of smaller diameter that will require smaller bearing surfaces creating less friction.
It is an object of this invention to provide a plug valve with a stationery lower stem to reduce o-ring wear and associated leakage issues.
It is an object of this invention to provide a plug valve that does not produce high velocity jets of fluids when valve is opened a small percentage, whereby the jets of fluid cause venturi effects that can dislodge o-rings from their seats, damage piping system from caviation and erosion to the ball valve components.
It is an object of this invention to provide a plug valve that has the capacity of up to 3000 Gallons per Minute and pressure differentials up to 100 psi but yet has the torque requirements of much smaller valves with minimal amounts of hysteresis.
It is an object of this invention to provide a plug valve whereby disassembly, repair and cleaning in the field of usage is accomplished with minimal effort where ball stems, stem seals and packing glands can be replaced without effecting the ball/o-ring interface.
It is an object of this invention to provide a plug valve whereby o-rings contain non-metallic components thereby reducing the possibility of corrosion, decomposition and failure.
It is an object of this invention to provide a plug valve whose inherent flow characteristics dictates that the Cv changes in an equal percentage manner over the travel range of the valve.
It is an object of this invention to provide a plug valve with equal percentage characteristics of flow and travel that does not exceed that which would be expected in a true linear relationship contrary to the quick-opening prior art valves that open more quickly than would be preferred in a linear equal percentage relationship.
It is an object of this invention to provide a plug valve that by retarding flow at lesser percentages of the travel range of the valve, thereby increases the efficiencies of the piping systems by creating a more linear relationship between valve opening percentage and percentage of heat transfer.
We meet these objectives with an approach as disclosed in the following detail description of the invention.